Method and apparatus for packaging glass substrates

ABSTRACT

Packages ( 11 ) of glass substrates ( 13 ) are provided in which the surfaces of the substrates are coated with a water-removable protective coating and then sealed in an air-sealing container ( 19 ), e.g., a polymer bag or a polymer wrapping, having an internal volume which is vacuumed, filled with an inert atmosphere, or filled with humidity-controlled air prior to sealing. In this way, the substrates can be stored for at least 6 months in an ambient environment having a relative humidity of 90 percent at 50° C. without substantial degradation of the protective coating.

FIELD OF THE INVENTION

This invention relates to glass substrates, such as the substrates used in the manufacture of liquid crystal displays (LCDs), plasma displays, electroluminescence displays, and the like. More particularly, the invention relates to methods and apparatus for packaging glass substrates so as to minimize damage during shipping and storage.

For purposes of illustration, the following discussion is in terms of glass substrates used in LCD displays, it being understood that the invention is equally applicable to glass substrates used in other applications.

BACKGROUND OF THE INVENTION

LCD manufacturing requires glass substrates having high quality surfaces. Particles, scratches, and organic contaminants are easily introduced onto glass surfaces during the finishing, storage, and transportation of LCD glass substrates. These glass surface defects can cause LCD circuit failure. Therefore, it is necessary to protect the glass surface during finishing, storage, and transportation.

Currently, a typical protection method is to coat LCD glass sheets with a polyethylene film with a pressure-sensitive adhesive on one side of the glass sheet and an electrostatic polymer film on the other. Prior to use, the protection films need to be peeled off, and then the glass surface cleaned to remove the adhesive and other loosely adsorbed contaminants. Aqueous cleaning is a preferred cleaning method for reasons of low cost, less environmental hazards, and effectiveness in removing both organic and inorganic contaminants. A typical aqueous cleaning process is a combination of ultrasonic cleaning and brush cleaning with an alkaline detergent, e.g., an aqueous solution of 2% SEMICLEAN KG.

While film coating can give satisfactory protection, it has a number of associated problems. First, the adhesive may not be completely removed due to variations in the coating process, and/or storage and transportation conditions, and/or variations in the cleaning process. Secondly, the film coating is applied after scoring of the glass bead from the edges of the newly formed glass. Thus, the film coating does not offer protection during bead scoring.

Thirdly, peeling off a film coating attached to a glass sheet with an adhesive may cause a high breakage rate for large glass sheets (e.g., 8′×6′) and/or thin glass sheets (e.g., ≦0.4 mm). Additionally, the film coating process and the materials employed therein are expensive. Therefore, film coating may not be the best or a universal choice for LCD glass protection.

Water-based coatings or water removable coatings are an alternative to film coatings for protecting LCD glass. Examples of water-based coatings can be found in commonly-assigned Foster et al., U.S. Pat. No. 6,233,972, Birch et al., U.S. Pat. No. 6,379,746, He et al., U.S. patent application Publication No. US 2003/0110800, and Hou et al., U.S. patent application Publication No. US 2003/0186065, the contents of each of which are incorporated herein by reference. As discussed in these references, a preferred location for applying protective coatings is at the bottom of the draw of a glass forming machine, e.g., a fusion draw machine, so that the coating is applied essentially immediately after the glass forms, thus minimizing the chances of contamination of the glass' surfaces.

Coatings of water removable materials have the advantage that they can be applied to the glass prior to bead scoring, e.g., by spray or dip coating, and thus are able to protect the surfaces of the glass during scoring, as well as thereafter during finishing, storage, and transportation. Removal of a water-based coating is normally easier than removal of an adhesive since the coating can be removed using a typical aqueous cleaning process and no peeling is needed. In addition, the coating material and process are generally less expensive than film coating.

Unfortunately, water removable materials are prone to undergo changes in their properties in the presence of water and moisture. For example, under the high humidity conditions which can occur during storage and transportation, e.g., ≧90% relative humidity at 50° C., coatings made of water-based materials tend to become tacky. Also, if the coated glass sheets are packed together using conventional paper separators between the sheets, the paper may stick to the coating under high humidity conditions so that it is difficult to separate the paper from the glass.

In addition to these problems, the surfaces of, for example, spray-coated glass sheets may not always be fully covered, e.g., the coating may include pin hole defects. High humidity can cause the formation of a chemical bond between glass chips and exposed glass areas, so that the chips are in essence not removable from the sheets.

A further problem with water removable coatings arises from the fact that microorganisms can grow on some of the biodegradable materials used for such coatings, e.g., starches. The growth of microorganisms depends on water activity, with high humidity normally promoting growth.

It can thus be seen that through a variety of mechanisms, high humidity conditions can result in glass surface defects for glass substrates coated with water-based coatings. The present invention is addressed to this problem. In particular, the invention is addressed to providing a practical, cost-effective solution to the problem of degradation of water-based coatings as a result of exposure to high levels of humidity and/or water during shipping and storage.

SUMMARY OF THE INVENTION

In accordance with a first aspect, the invention provides a method for packaging glass substrates, e.g., LCD glass sheets, for storage and transportation under high humidity conditions, each substrate having two substantially flat surfaces which are coated with a water-removable protective coating, said method comprising in order:

-   -   (A) stacking the coated glass substrates to form a block; and     -   (B) packaging the block in a container (e.g., an air-sealing         polymer bag or polymer wrapping) having a sealed internal         environment which protects the water-removable protective         coating from humidity-based degradation.

The substrates when initially stacked to form the block will have exposed corners and edges. In the preferred embodiments of the invention, prior to step (B), the exposed corners and/or at least some of the exposed edges of the substrates are protected using cushioning material (preferably, both the corners and at least some of the edges are protected with cushioning material).

In accordance with a second aspect, the invention provides a package of glass substrates comprising:

-   -   (A) a plurality of glass substrates arranged in a block, each of         said substrates having two substantially flat surfaces which are         coated with a water-removable protective coating; and     -   (B) a container (e.g., an air-sealing polymer bag or polymer         wrapping) which surrounds the block and forms a sealed internal         environment which protects the water-removable protective         coating from humidity-based degradation.

As in the first aspect, the package of glass substrates preferably also includes cushioning material applied to the corners and/or at least some of the edges of the substrates (preferably, cushioning material is applied to both the corners and at least some of the edges).

Additional features and advantages of the invention are set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating an air-sealing packaging of stacked glass in accordance with the invention.

FIG. 2 is an expanded, schematic, cross-sectional view of the upper right corner of FIG. 1.

The reference numbers used in the drawings correspond to the following:

-   -   11 package of glass substrates     -   13 glass substrate     -   15 soft cushioning material     -   17 separator     -   19 container (e.g., air-sealing film)

DETAILED DESCRIPTION OF THE INVENTION

As discussed above, the present invention provides methods and apparatus for limiting the exposure of glass sheets (glass substrates) with a water removable coating to moisture either in the form of liquid water or high humidity.

In outline, the substrates with a water removable protective coating are stacked and then packed in an air-sealed container, e.g., an air-sealed polymer, which allows for the formation of an internal environment having a controlled moisture content. For example, the stacked glass sheets can be sealed in a container, e.g., a polymer bag or wrapping, from which air has been removed (vacuumed) and/or the packing can be performed in a controlled humidity environment (e.g., an environment that has a relative humidity less than 50%, preferably less than 40%, more preferably less than 30%, and most preferably less than 20% at a temperature less than 50° C., more preferably less than 30° C.) so that the air which does become sealed in the container has a predetermined, desired humidity. Alternatively, an artificial environment can be introduced into the container, e.g., an inert gas such as nitrogen or argon can be introduced into the container prior to sealing.

An air-sealing bag or wrapping which generally conforms to the shape of the block of glass substrates is preferred since it minimizes the chances of particles coming into contact with the surfaces of the glass sheets during shipping or storage. If desired, the block of substrates in the air-sealing bag or wrapping can be placed in a rigid shipping container, e.g., a container made of wood, to provide further mechanical protection for the glass sheets. Alternatively, instead of a flexible bag or wrapping, the air-sealing container can be rigid. For example, the block of glass sheets can be placed directly in an air-sealing container composed of metal, e.g., a sealable aluminum container. Depending on the strength of the metal or metal alloy used and the size of the block of glass sheets, the sealed container can be shipped and stored as is or can be placed in a non-sealed external container, e.g., a wooden container, which provides sufficient structural integrity to withstand the forces typically encountered during shipping and storage.

Because of the low humidity conditions which are achieved in the container, however formed, glass sheets coated with a water removable material do not stick to one another or to separators between the sheets during storage and transport. Similarly, chemical binding of glass particles to exposed glass surfaces is minimized and the coatings exhibit enhanced microorganism resistance.

Another advantage of the invention is that it expands the range of protective coatings which can be used on glass substrates to include hygroscopic materials which otherwise would be unsuitable for use in this application. Such materials can be used because the air-sealed packing protects their integrity when in high humidity environments, e.g., when glass sheets are undergoing transoceanic shipping. Hygroscopic materials are desirable as protective coatings because they are easily removed by water when the glass substrate is to be used to produce, for example, an LCD device.

In the preferred embodiments of the invention, the air-sealed container should allow glass sheets with a water removable coating to be stored in or transported through a humid environment having a relative humidity of more than 90% at 50° C. for at least 6 months.

A variety of water-soluble protective coatings can be used in the practice of the invention, including, without limitation, polysaccharides, polymeric acids, polyvinyl alcohols, polypropylene oxide-polyethylene oxide copolymers, surfactants, and mixtures of two or more of the foregoing. Among the polysaccharides that can be used are starch products, methylcelluloses, hydroxypropyl methylcelluloses, hydroxyethyl methylcelluloses, and alginates. Among the polymeric acids that can be used are polyacrylic acids and poly(methyl vinyl ether—alt—maleic acids). The foregoing list of coating materials is not exhaustive but rather is only illustrative.

The protective coating is preferably removable from the glass substrate using an aqueous cleaning method, such as ultrasonic cleaning combined with brush cleaning or brush cleaning alone using an alkaline detergent (e.g., a 2% aqueous solution of SEMICLEAN KG) at 25° C. to 80° C., preferably 40° C. to 75° C., more preferably 55° C. to 75° C.

The coated glass sheets can be stacked together with our without separators between the individual sheets. If separators are used they can be made out of paper or polymer films. Whether separators are used or not, the corners and/or at least some of the edges of the glass sheets are preferably protected with a soft cushioning material which can be, for example, a natural or man-made polymer fiber, a natural or man-made fiber mixture, a fabric made of a natural or man-made polymer or a natural or man-made polymer mixture, or combinations of the foregoing. Examples of natural polymers that can be used for the cushioning material include cotton, wood, ramie, wool, silk, and linen, and examples of man-made polymers include polyacetate, polyester, polyamide, cellulose acetate, acrylic, rayon, cupro, laster, and modal.

The materials used for making the air-sealed packing can be any material or combination of materials that will produce an air tight container. As discussed above, the air-sealed packing is preferably a bag or wrapping. Such containers can be made of any polymer that forms a flexible, air tight film, and is preferably sufficiently durable to withstand the conditions normally encountered during storage and transportation with a minimum of additional protective materials. Examples of suitable polymers include polyethylene, polypropylene, poly(vinyl chloride), poly(ethylene terephthalate), nylon and TEFLON. Sealing of such polymer films to form the air-sealed packing can be performed using various methods known in the art. Illustrative examples include partially melting the polymer and the use of a water resistant glue. In the case of rigid containers, sealing can be achieved using known methods in the art, e.g., gaskets, external wrappings, etc.

FIGS. 1 and 2 show an example of an air-sealing packing 11 constructed in accordance with the invention. Glass sheets 13 coated with a water removable material are stacked together to form a block. As shown in these figures, separators 17 (e.g., paper or polymer sheets) are used between the individual glass sheets. If desired, the separators can be omitted.

The corners and at least some of the edges of the glass sheets making up the block are protected by a soft cushioning material 15. Specifically, in FIGS. 1 and 2, all of the corners are protected as well as the top and bottom edges, but only parts of the side edges come into contact with the cushioning material. The cushion not only protects the glass corners and/or edges, but also prevents cutting of the polymer wrappings when used.

Once the edges and/or corners have been protected, the stacked glass sheets are sealed in air-sealing container 19, e.g., an air-sealing polymer film. As discussed above, air in the packing can be removed prior to the sealing, or the packing can be sealed in a humidity controlled environment (e.g., an environment having a relative humidity of 25% at 25° C.) without air removal. As a further alternative, one or more inert gases, e.g., nitrogen and/or argon, can be used to replace the air in the air sealing packing.

Glass sheets packed in this way can be stored at high humidity for a long time, e.g., at a relative humidity of 90% at 50° C. for over a year, without the creation of surface defects as a result of the humid environment.

Without intending to limit it in any manner, the present invention will be more fully described by the following examples.

EXAMPLE 1

Glass sheets are dip-coated with 10% CRYSTAL TEX 627 (National Starch and Chemical Company, Bridgewater, N.J.) with 0.15% sorbic acid. The coated glass sheets are stacked together with brown paper. The stacked glass sheet block is wrapped with cleanroom cloth on the edges. Then, the glass sheet block is placed into a poly(ethylene terephthalate) bag. The bag is sealed in a temperature and humidity controlled environment which is at 25° C. and 25% relative humidity.

EXAMPLE 2

Glass sheets are spray-coated with 5% poly(acrylic acid) with 0.15% sorbic acid. The coated glass are stacked without a separator. The stacked glass sheet block is protected by cotton on each corner. Then, the block is wrapped with polyethylene film. The wrapping is completely sealed after the air is removed.

From the foregoing it can be seen that the invention provides packages and packing methods that: (1) protect the integrity of water-removable coatings, (2) prevent sticking of such coatings, (3) reduce water interaction with uncoated glass areas, and (4) eliminate or at least control microorganism growth.

Although specific embodiments of the invention have been described and illustrated, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the invention's spirit and scope. The following claims are thus intended to cover the specific embodiments set forth herein as well as such modifications, variations, and equivalents. 

1. A method for packaging glass substrates for storage and/or transportation, each substrate having two substantially flat surfaces which are coated with a water-removable protective coating, said method comprising in order: (A) stacking the coated glass substrates to form a block; and (B) packaging the block in a container having a sealed internal environment which protects the water-removable protective coating from humidity-based degradation.
 2. The method of claim 1 wherein said substrates when stacked have exposed corners and edges and said method comprises protecting the exposed corners and/or at least some of the exposed edges of the substrates using cushioning material prior to step (B).
 3. The method of claim 2 wherein both the exposed corners and at least some of the exposed edges of the substrates are protected using cushioning material.
 4. The method of claim 1 wherein the container is an air-sealing polymer bag or polymer wrapping.
 5. The method of claim 1 wherein the coated glass substrates are stacked together using separators between the substrates.
 6. The method of claim 1 wherein the internal volume within the container is vacuumed prior to sealing.
 7. The method of claim 1 wherein the internal volume within the container is filled with an inert gas or an inert gas mixture prior to sealing.
 8. The method of claim 1 wherein the internal volume within the bag or wrapping is sealed in a controlled humidity environment.
 9. The method of claim 8 wherein the controlled humidity environment has a relative humidity of less than 50% at a temperature less than 50° C.
 10. The method of claim 1 wherein the water-removable protective coating is protected from degradation for at least 6 months in an ambient environment having a relative humidity of 90 percent at 50° C.
 11. The method of claim 1 comprising the additional steps of: removing the glass substrates from the container; and removing the water-removable protective coating from the glass substrates using an aqueous cleaning method.
 12. The method of claim 11 wherein the aqueous cleaning method includes washing the glass substrates in an aqueous solution of an alkaline detergent whose temperature is between 25° C. and 80° C.
 13. A package of glass substrates comprising: (A) a plurality of glass substrates arranged in a block, each of said substrates having two substantially flat surfaces which are coated with a water-removable protective coating; and (B) an air-sealing container surrounding the block, said container forming a sealed internal environment which protects the water-removable protective coating from humidity-based degradation.
 14. The package of glass substrates of claim 13 wherein the substrates when stacked have exposed corners and edges and said package further comprises cushioning material applied to the exposed corners and/or at least some of the exposed edges of the substrates.
 15. The package of claim 14 wherein cushioning material is applied to both the exposed corners of the substrates and at least some of the exposed edges.
 16. The package of claim 13 wherein the container is an air-sealing polymer bag or polymer wrapping.
 17. The package of claim 13 further comprising separators between the substrates.
 18. The package of claim 13 wherein the sealed internal environment is at a pressure below atmospheric pressure.
 19. The package of claim 13 wherein the sealed internal environment contains an inert gas or an inert gas mixture.
 20. The package of claim 13 wherein the sealed internal environment contains air which has a relative humidity of less than 50% at a temperature less than 50° C.
 21. The package of claim 13 wherein the water-removable protective coating is protected from degradation for at least 6 months in an ambient environment having a relative humidity of 90 percent at 50° C.
 22. The package of claim 13 wherein the glass substrates are LCD glass substrates. 